2 research outputs found
Ecological interactions in Cloudina from the Ediacaran of Brazil : implications for the rise of animal biomineralization.
At the Ediacaran/Cambrian boundary, ecosystems witnessed an unparalleled biological innovation:
the appearance of shelled animals. Here, we report new paleoecological and paleobiological data on
Cloudina, which was one of the most abundant shelled animals at the end of the Ediacaran. We report
the close association of Cloudina tubes with microbial mat textures as well as organic-rich material,
syndepositional calcite and goethite cement between their flanges, thus reinforcing the awareness of
metazoan/microorganism interactions at the end of the Ediacaran. The preservation of in situ tubes
suggests a great plasticity of substrate utilization, with evidence of different life modes and avoidance
behavior. Geochemical analysis revealed walls composed of two secondary laminae and organic sheets.
Some walls presented boreholes that are here described as predation marks. Taken together, these data
add further information regarding the structuring of shelled animal communities in marine ecosystems
Geobiological and diagenetic insights from Malvinokaffric devonian biota (Chapada Group, Paran? Basin, Brazil) : paleobiological and paleoenvironmental implications.
This study tests the presence of differential preservation in the Devonian Malvinokaffric fauna from the
Chapada Group (Parana? Basin, Brazil). Results of EDXRF, EDS, Raman Spectroscopy, and petrographic analyses
show differential preservation of shells that were originally calcite as hematite and goethite fossils, while organisms
with original calcium phosphate shells tend to be preserved inside phosphatic concretions. Both preservation types are
commonly associated with pseudoframboids, while calcium sulfate minerals are commonly associated with hematized
fossils. From this evidence, a diagenetic model for these fossils is proposed. The model includes an early diagenetic
phase (characterized by anaerobic sulfate reduction and precipitation of pyrite and carbonate-fluorapatite) and a
second, near-surface chemical weathering phase (characterized by the oxidation of pyrite and precipitation of iron
oxyhydroxides and calcium sulfates). Acidic conditions in both phases may account for the dissolution of less stable
minerals compared to calcium phosphate. It is considered that this model may assist in understanding other similarly
preserved biotas, as well as enhancing understanding of the taphonomic overprint that may occur within this
important and endemic Devonian biota